1. Field of the Invention
The present invention relates to a control device for cables with seismic equipment, especially for seismic gun cables provided with one or several arrays of guns which are towed behind a vessel. The term gun cable in this context covers both a cable and one or more gun arrays. The invention especially relates to a control device for maintaining a gun cable in a course of travel that is laterally displaced in relation to the course of travel of the vessel towing the cable in the sea.
2. Description of the Prior Art
In seismic exploration at sea seismic gun cables, i.e. cables comprising pulse emitting "guns" suspended beneath buoyancy members, are towed in the water behind a vessel. From the guns pulses are fired, the reflections of which from the sea bottom are detected by the aid of a receiver cable, or streamer, that is also towed behind the vessel.
There are a number of different principles for designing such towing systems for seismic exploration in order to achieve the best possible results based on local conditions and geological formations. In this connection it may, inter alia, be desirable to tow several cables side by side in a parallel formation with defined interspaces. Such a method for several parallel gun cables is, e.g. disclosed in Norwegian Pat. No. 147.655 (Application No. 80 3400), which corresponds to U.S. Pat. No. 4,506,352. In the method disclosed in that reference otter boards and paravanes (float bodies) are used to space the cables mutually. With this method a comparatively wide distribution of cables may be achieved, e.g. a distance of 150 m between the outermost cables. It has also been suggested to use floats with rudder control to keep cables at a mutual distance, but float arrangements of this kind will be dependent on both weather and wind, and it is a question how efficient they would really be.
In case of the method disclosed in the above mentioned patent a smaller distance between gun cables laterally may be sufficient for special conditions or geological formations. This may also be the case when smaller areas and narrow or shallow waters are to be explored, and a simplified equipment for keeping said cables at a mutual lateral distance will obviously, be advantageous in such cases. There is, thus a demand for a simple device to be used for carrying out the method according to the above mentioned patent in a limited or smaller area.